There are several synonyms for the phrase "being insincere with." Some common ones include "being dishonest with," "lying to," "deceiving," and "misleading." All of these phrases describe actions in which one person intentionally misrepresents their thoughts or feelings to another person. Other synonyms for being insincere with may also include "pretending," "hypocrisy," and "phoney." It is important to avoid being insincere with others, as it can damage relationships, cause misunderstandings, and lead to a lack of trust. By being truthful and transparent in our interactions with others, we can build stronger connections and foster stronger bonds of trust and respect.